StripeCompactionPolicy should support compacting cold regions

Cold regions cannot perform compactions by flushing memstores, while CompactionChecker can period check need compaction regions.

But some cold regions using stripe store engine may not be checked to perform compaction by`needCompaction()` or trigger automatic major compactions, because StripeCompactionPolicy#shouldPerformMajorCompaction() always returns false. 

StripeCompactionPolicy never performs automatic major compactions now.

But cold regions' outdated data need to be cleaned.